Method of manufacturing metal electric rectifiers



Set. 30, 1947.

METHOD OF MANUFACTURING METAL ELECTRIC RECTIFIERS Filed Aug. 16, 1943 A. M. SEARLE 2,428,043 C Patented Sept. 30, 1947 7.

, METHOD OF MANUFACTURING METAL ELECTRIC RECTIFIERS Arthur Mackenzie Searle, London, England,-as-

signer, by mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation ofDelaware Application August 16, 1943, Serial'No; 498,753

The present invention relates to the manufacture of metal rectifiers used for electrical alternating current circuits, but more particularly to the manufacture of instrument rectifiers where a very high reverseimpedance may be required.

The metal rectifier is well known to consist of Figs. 3 and 4 show the shapes of two spraya metal disc or base to one surface of which is ingmasks used in manufacturing the rectifier. applied a layer of rectifyin material (such as The rectifier shown in Figs. 1 and 2 comprises selenium or copper oxide or the like). A metal a metal base I having on its upper surface a surface electrode is sprayed or otherwise applied 10 layer 2 of rectifying material (selenium, copper to the upper surface of the rectifying material to oxide, etc ,On the upper surface of the rec: make contact therewith. When it is desired tifying material is sprayed a layer or coating 3 of that the impedance of the rectifier in the backinsulating material which is circular except for ward direction shall be very high, say of the ortwo approximately rectangular areas 5, 6, symder f. 1 megohm, the area of the rectifying mametrically placed on either side of, and project terial must be made very small, for example, of mg towardathecentre of the disc. the order of one. or two square millimetres; and A conducting circular surface electrode 4 of in order to avoid the dilfi'CllltleS associated with smaller cliameter is thensprayed. on top of the handling very small parts in manufacture, it is insulating layer and makes contact with the rec usual to employ discs of considerably larger area tifying layeronly over the approximately recthan would otherwise be necessary, and to coat tangular areas 1 and 8 which together define the or render active only a relatively small proporactive area of the rectifier. Contact may be tion of the area. As it is also common prace w t the surface electrode 4 i y tice to spray the coatings through masks it is venient way, not shown. found that unless special care is taken to clean The insulating coating 3 is sprayed on to the the masks after each spraying operation a prorectifying layer 2 through a mask 9, shown in gressive change in the area defined by the mask Fig. 3, whi h Consists f a thin plate having it occurs because the mask itself becomes coated circular hole with a diameter equal to the dewith the spraying material which spreads over sired diameter of the layer 3, but having two the edges thus tending to increase the area inwardly p ojecting r ta u ar n es 5 and blocked out. This may result in very large perl6, which define the areas 5 and 6 which are centage changes in the active area of a small inleft uncoated. It will be evident that if the strument rectifier. mask 9 is used for spraying a large number of The present invention seeks to overcome this rectifiers in succession without cleaning the difiiculty by a manufacturing process in which t g deposited n the k W grad y it is not necessary to clean the masks after each enlarge the effective area of the tongues 15 and spraying operation the coatings being so shaped 50 a Unless app p a measures a e taken. that the progressive changes occurring in one the active areas I and 8 of successively manufac mask are compensated by similar changes occurtured rectifiers will increase, and may soon bering in another subsequently used mask. come reat r t he pe i i le limit.

The invention accordingly comprises the According to the invention, the surface elecmethod of manufacturing successively a pluraltrode 4 is spr yed on top of th ins ti lay r ity of metal rectifiers which for each rectifier through another mask l0 shown in Fig. havin comprises applying a layer of rectifying matea circular hole equal in diameter to that desired rial to a base, spraying an insulating coating for the electrode. If this mask is used continuthrough a first mask on to the rectifyin layer, ously without cleaning, the deposit thereon will and then spraying a conducting coating thereon pr ssively reduce the area of the Central h through a second mask; the masks being so deand this will progressively reduce the distance signed and located for spraying that the conductfrom the centre of the outer edges of the active ing coating makes contact with the rectifying areas I and 8. This, it will be seen, is in the layer over tWo or more isolated areas the sum of direction to comp f r he Pr r ive inwhich is substantially independent of the proreas n th un at d a a 6 d t t gressive changes in the coating areas of successive changes in the mask 9. By u a y e s o rectifiers which result from the coating of the ing the coatings 3 and 4, the two effects may be masks by the spraying material. made to neutralize one another, so that the active In Great Britain October 2, 1942 5 Claims. (01. 117-'-38) v 2 The invention will be described with reference to the accompanying drawing in which:

Fig. 1 shows a plan view of a metal rectifier manufactured according to the invention;

Fig. 2 shows an elevation of the rectifier; and

, c 3 areas 1 and 8 on different rectifiers remain practically constant in a batch coated in succession without cleaning the masks.

It will be evident that the surface of the rectifying material may be divided up into more than two active areas, if desired, by providing-a mask 9 havingany number of similar inwardly projecting tongues like l5 and [6, but they should preferably be symmetrically arranged round the centre. With any number of such areas, it will only be necessary to register the masks 9 and I approximately correctly, for with a small amount of eccentricity, although the active areas like and 8 will not all be equal, their sum will not ,be

much changed, since some will be increased'and L substantially rectangular in shape which are unothers decreased; and moreover, the compensating efiect will likewise be little affected.

It will be apparent, therefore, that the process described will enable a series of rectifier-s to be manufactured within relatively close limits without the necessity for constant cleaning of the masks 9 and 10 or for accurate registration thereof, bothof which requirements have hitherto been sources of increased cost in the manufacture of largequantities of rectifiers.

What is claimed is:

1. The method of manufacturing successively a pluralityof metal rectifiers which for each rectifier comprises; applying a layer of rectifying material to a base, spraying'an insulating coating througha first mask on to the rectifying layer, and then spraying a conducting coating thereon through a second mask; the masks being so designed and located for spraying that the conduct ing coating makes contact with the rectifying layer over two or more isolated areas, the sum of which is substantially independent of the progressive changes in the-coating areas of succes- Si Ve: rectifiers'which resultfrom the coating of the masks by the spraying material.

coated.-

5. The method of manufacturing successively a plurality of rectifiers which for each rectifier comprises: applying a layer of rectifying material to a base; applying a coating of insulation on the rectifying layer through a mask which has an enclosed opening into which an area of the mask projects; and then applying a conduct= ing coating through a second mask having an enclosed opening made to overlie the insulating coating and at leasta portion of said projecting area.

ARTHUR MACKENZIE SEARLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

